Systems and methods providing transmit diversity to combat multipath effects in position estimation

ABSTRACT

Described are systems and methods for estimating a position of receiver using co-located transmitters.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to co-pending U.S. Provisional Patent Application Ser. No. 61/786,544, filed Mar. 15, 2013, entitled SYSTEMS AND METHODS PROVIDING TRANSMIT DIVERSITY TO COMBAT MULTIPATH EFFECTS IN POSITION ESTIMATION, the content of which is hereby incorporated by reference herein in its entirety for all purposes.

FIELD

Various embodiments relate to providing transmit diversity.

BACKGROUND

There is a need for improved position estimation techniques that combat multipath effects

SUMMARY

Certain embodiments of this disclosure relate generally to estimating a receiver's position based on range measurements associated with co-located transmitters.

DRAWINGS

FIG. 1 depicts aspects of a terrestrial positioning system.

FIG. 2A depicts aspects of a system with sets of co-located transmitters.

FIG. 2B depicts aspects of a set of co-located transmitters.

FIG. 3 illustrates a process for estimating the position of a receiver.

DESCRIPTION

Various aspects of the invention are described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both, being disclosed herein is merely representative. Based on the teachings herein one skilled in the art should appreciate that any aspect disclosed may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, a system may be implemented or a method may be practiced using any number of the aspects set forth herein.

As used herein, the term “exemplary” means serving as an example, instance or illustration. Any aspect and/or embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects and/or embodiments.

In the following description, numerous specific details are introduced to provide a thorough understanding of, and enabling description for, the systems and methods described. One skilled in the relevant art, however, will recognize that these embodiments can be practiced without one or more of the specific details, or with other components, systems, and the like. In other instances, well-known structures or operations are not shown, or are not described in detail, to avoid obscuring aspects of the disclosed embodiments.

Overview

Various aspects, features, and functions are described below in conjunction with the appended Drawings. While the details of the embodiments of the invention may vary and still be within the scope of the claimed invention, one of skill in the art will appreciate that the Drawings described herein are not intended to suggest any limitation as to the scope of use or functionality of the inventive aspects. Neither should the Drawings and their description be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in those Drawings.

One of the major challenges that ground-based “time-of-arrival” (TOA) positioning systems encounter in urban/indoor environments is the severe wireless signal multipath effect caused by the low-elevation nature of the terrestrial transmitters and environmental objects disposed between the transmitters and a receiver. Before reaching the receiver, a wireless ranging signal transmitted from a transmitter is possibly reflected, diffracted and/or scattered by single/multiple surrounding objects (such as buildings and vehicles) and arrives at the receiver with a certain time delay compared to the “line-of-sight” (LOS) signal.

Measurements of the travel time for the signal between a transmitter and a receiver may be used as a measure for the distance over which the signal traveled, but that distance is not always an accurate reflection of the LOS distance between the transmitter and the receiver because of the multipath effect. Moreover, combined received signals, including signals traveling over direct LOS pathways and multipath-delayed pathways, generate difficulties for the receiver to retrieve the earliest arriving LOS signal, as well as estimate the transmission time associated with the signal. This directly causes a range measurement error, based on which the calculated trilateration positioning solution is erroneous as well. In extreme situations, such as dense urban canyon or deep indoor locations, the direct LOS signal is totally attenuated by the objects between the transmitter and the receiver so that it is impossible to obtain an accurate range measurement by investigating the received signal delay profile alone. In some cases, reflected pathways due to the multipath effect may be a few hundred meters longer than the LOS pathway.

The above-mentioned problems can be combated at several levels. For example, transmitters could be placed at higher altitudes to increase the likelihood of LOS signal transmission. Alternatively, super-resolution, trilateration or other algorithms may be modified to increase likelihood of seeing a LOS signal or to better handle multipath signals. However, improvements to algorithms may not sufficiently address these problems, and deployment of higher-altitude transmitters may not be feasible.

One solution to these and other problems is to provide groups of two or more co-located transmitters, where the co-located transmitters are separated by a relatively short distance from each other (e.g., 2-5 meters in some embodiments) as compared to distances that separate each group of co-located transmitters. Disclosure herein may relate to pairs of co-located transmitters; however, any number of co-located transmitters is possible. Also, the co-located transmitters may be connected to separate co-located beacons, or may be connected to a single beacon capable of supporting multiple co-located transmitters. In the preferred embodiment, the co-located transmitters use the same time slot, and use a different PRN and frequency offset, though in other embodiments other combinations of slot/PRN/frequency offset might be chosen for the co-located transmitters.

Signals from each co-located transmitter may be used to detect whether either signal or both signals are LOS signals or multipath (MP) signals. LOS signals may be weighted more than MP signals. Or, MP signals may be removed from trilateration processing. In some embodiments, an estimate of the length of the MP signal pathway may be made, and then used directly in the trilateration algorithm, thus improving performance.

Terms

This disclosure may use various terms, including “time-of-arrival (TOA)” and “range”. The terms are related in that “TOA” represents travel time of a signal while “range” represents a distance that can be computed using the TOA and the signal speed (e.g., speed of light). The term “range measurement” or “pseudorange” may be generally used to refer to timing data. Broadly speaking, “timing data” as used herein may comprise data associated with a signal pathway range, including the signal's travel time (i.e., time of arrival) over the pathway.

The term “LOS signal” may be used herein to denote a signal that reaches a receiver after traveling along a LOS signal pathway from a transmitter. Similarly, the term “multipath signal” may be used herein to denote a signal that reaches a receiver after traveling along a multipath signal pathway from a transmitter.

Trilateration may include a process by which ranging results are combined for various transmitter's to estimate a receiver's location. Trilateration usually involves assigning weights to ranging results from each transmitter. There may also be an individual bias (or adjustment) made to ranging results from each transmitter. During trilateration, a set of candidate locations are considered, and a location that best fits the data is selected. Each candidate location is a triplet of the form (x,y,z), usually in an ENU coordinate system. Disclosure below relates to methodologies applied in relation to an individual candidate position. One of skill in the art will appreciate that any of the methodologies herein may be applied to multiple candidate positions. By way of example, one algorithm for trilateration may be defined as follows:

F(x,y,z,t _(—) b)=minsum(w _(—) k*abs(p _(—) k−r _(—) k(x,y,z)−t _(—) b){circumflex over (α)}p),

where w_k is the weight of the k̂th transmitter, p_k is the pseudorange of the k̂th transmitter, r_k(x,y) is the distance of the candidate location (x,y) to the k̂th transmitter, t_b is the time bias, z is the receiver height, and p is the power to which we raise the error (e.g., p is usually 2 in the literature; however, in one embodiment, p is 1 due to superior performance in the presence of multipath).

Attention is now made to the drawings, which depict various aspects of the disclosure. It is noted that similar numbers are used to designate aspects that share similar characteristics. For example, reference could be made to a system 100A through system 100E, which each comprise similar components while depicting five different embodiments. It is further noted that one number may be used to simultaneously refer to similar aspects. For example, reference to component 10 may refer to any of components 10 a-n.

Systems Using Co-Located Transmitters to Determine Position Estimate

As illustrated in FIG. 1, a system 100 may comprise a terrestrial transmitter network comprising transmitters 111, 113,115 and 117 positioned among various terrestrial objects 190 (e.g., man-made objects like buildings and cars, or natural objects like hills, vegetation, and reflective surfaces like water). The transmitters 111-117 may be configured to provide timing data. The timing data may then be used by the receiver 120 or a server (not shown) to compute an estimate of the receiver 120's position.

In urban environments, like the one depicted in system 100, the travel time for a signal is subject to “multipath” delays where the signal does not follow a straight path between a transmitter and the receiver 120, and instead travels around various objects 190. By way of example, a signal from transmitter 111 to the receiver 120 may follow a line-of-sight signal pathway 131 a or a multipath signal pathway 131 b. In some cases, as shown by signal pathway 135 associated with transmitter 115, a signal may only reach the receiver 120 after traveling “around” objects 190. Still, in certain cases, as shown by signal pathway 137 associated with transmitter 117, some signals may never reach the receiver 120.

Attention is now drawn to FIG. 2A, which shows a system 200 with co-located transmitter pairs 211 a & 211 b, 213 a & 213 b, 215 a & 215 b, and 217 a & 217 b. Each transmitter transmits a signal that travels along a corresponding signal pathway. For example, signals from transmitters 211 a & 211 b may travel along signal pathways 231 a & 231 b, respectively. Similarly, signals from transmitters 213 a, 213 b, 215 a, 215 b, 217 a and 217 b may travel along signal pathways 233 a, 233 b, 235 a, 235 b, 237 a and 237 b, respectively.

As shown, some signal pathways are line-of-sight (LOS) pathways, including signal pathways 231 a, 233 a and 233 b. Remaining signal pathways are multipath signal pathways. Some of these multipath signal pathways correspond to considerable time delay with respect to a LOS distance between the corresponding transmitter and the receiver 120. For instance, the receiver 120 may receiver a signal from transmitter 215 a that travels around various objects over a signal pathway 235 a that is considerably longer than a LOS distance indicated by 245 a.

FIG. 2A also illustrates that a signal from transmitter 217 a never reaches the receiver 120 along signal pathway 237 a.

To further illustrate multipath characteristics related to co-located transmitters, attention is now drawn to FIG. 2B. As shown in FIG. 2B, a first transmitter 210 a (Tx1) and a second transmitter 210 b (Tx2) are co-located at a position that is remote from a receiver 120(Rx). FIG. 2B shows a LOS distance (d₁) between the first transmitter 210 a and the receiver 120, and a LOS distance (d₂) between the second transmitter 210 b and the receiver 120. The LOS distances may be determined by computing a vector distance between position coordinates (e.g., latitude, longitude, altitude) of each transmitter 210 a and 210 b and corresponding position coordinates of the receiver 120.

Further shown in FIG. 2B is a MP distance (d_(1MP)) between the first transmitter 210 a and the receiver 120, and a MP distance (d_(2MP)) between the second transmitter 210 b and the receiver 120. The MP distances may each correspond to multipath signal pathways corresponding to signals that reflect off of object 190. Ranging information (e.g., time-of-arrival information) may be used to calculate the distances.

Alternatively, any distance may be converted to travel time or some other timing/range data associated with ranging measurements taken by the receiver 120.

In some cases, d₁ may be shorter than d₂, but d_(1MP) may be longer than d_(2MP). Relationships of individual measurements per transmitter may further help map obstructions and multipath errors.

For pairs of co-located transmitters, a difference between the LOS distances (referred to as Delta-LOS) may be calculated, and then compared to a calculated difference between distances relating to received ranging signals (referred to as Delta-RANGE), which may include LOS signals or MP signals. Calculating the Delta-RANGE may advantageously eliminate time bias.

Alternatively, since Delta-LOS is relatively small (e.g., up to 5 meters in some embodiments), the value of Delta-LOS may be set to zero (0). As stated above, distances need not be used. Instead, other timing/range data like time-of-arrival data may be compared.

Once calculated, Delta-RANGE may be used to identify whether its value is more likely to result from two LOS signals or at least one MP signal. In one embodiment, for a given candidate receiver location estimate, the receiver 120 may calculate Delta-LOS for that candidate location estimate (e.g., based on the position coordinates of each co-located transmitter, and position coordinates of the candidate position of the receiver 120). That value of Delta-LOS may then be compared to a Delta-RANGE value to determine how similar or dissimilar the measured values are from each other.

In some cases, if the observed Delta-RANGE from ranging results received by a receiver 120 is greater than Delta-LOS by a threshold margin (e.g., a predefined number of units), then at least one of the ranging results resulted from a MP signal, and a weight or adjustment may be selected based on the difference and subsequently applied during trilateration processing (e.g., by weighting the ranging results or adjusting them by some value). It may even be possible to estimate, to a degree, the extra length of the multipath signal from the relationship between Delta-RANGE and Delta-LOS.

Alternative embodiments are described in more detail below with respect to different methodologies for using co-located transmitters to determine a position estimate.

Methodology Using Co-Located Transmitters to Determine Position Estimate

Various aspects can be combined to form different embodiments where a trilateration algorithm can be influenced in many ways. For example, the relationship between Delta-RANGE and Delta-LOS may be exploited in many ways, including comparing the ratio and/or difference of these two quantities against some thresholds to perform various functions, including selection of a range measurement for a particular transmitter, altering weights applied to a range measurement, or adding a different time bias to a range measurement in association with application of the trilateral algorithm. In particular, the relationship between Delta-RANGE and Delta-LOS at each candidate position may be used to calculate different trilateration metrics (e.g. weights applied to range measurements, biases applied to range measurements, and selection of range measurements used).

Alternatively, Delta-LOS may be assumed to be equal to zero (0) to thereby avoid having to calculate Delta-LOS for each candidate receiver location, and Delta-RANGE may be used to select weights and adjustments to range measurements before the range measurements are used during trilateration computations.

Alternatively, an initial estimate of the receiver location—e.g., (x₀,y₀,z₀)—may be determined and used that estimate to calculate trilateration metrics that will be used for particular candidate locations or all candidate positions.

In support of trilateration processing, adjustments to range measurements (PR) and corresponding weights (W) may take the form of:

PR _(New(k)) =PR _(Measured(k)) −PR _(Adjustment(k)), and W _(New(k)) =W _(Selected(k)) *W _(Adjustment(k)),

where PR_(Measured(k)) is the range measurement, PR_(Adjustment(k)) is the amount used to adjust the range measurement, PR_(New(k)) is the adjusted range measurement, W_(Selected(k)) is a weight applied to the range measurement, W_(Adjustment(k)) is the amount used to adjust the weight, and W_(New(k)) is the adjusted weight. In some embodiments, the value of PR_(Adjustment(k)) may take on a value greater than zero (0), while the W_(Adjustment(k)) may take on a value between zero (0) and one (1). The “k” references a particular transmitter from a set of transmitters 1 through n.

Selection of range measurements, adjustments to range measurements, weights, and adjustments to weights may be determined based on various aspects.

For example, where range measurements are received for both co-located transmitters, the shortest range measurement may be selected for use during trilateration because it may be assumed that the shorter range measurement is more accurate than that longer range measurement (which is assumed to be a multipath measurement). Accordingly, the longer range measurement may be omitted from trilateration processing (e.g., by selecting a weight of zero or adjusting a weight to zero), or its weight may be reduced because it is less accurate as a measurement of LOS distance than the shorter range measurement. Alternatively, the weight of the shorter range measurement may be increased because it is more accurate than the longer range measurement.

Alternatively, the value of the shorter range measurement may be used to adjust the value of the longer range measurement. For example, the longer range measurement may be set to the value of the shorter range measurement (e.g., by subtracting the difference between the two range measurements from the longer range measurement, or by replacing the value). The adjusted longer range measurement may then be used during trilateration based on selected weights, or adjusted weights as described elsewhere herein.

Alternatively, the range measurement may be adjusted based on the Delta-RANGE value. For example, the Delta-RANGE value may be subtracted from the shorter measurement or the longer range measurement. In another embodiment, some fraction or multiple of the Delta-RANGE value may be used to adjust (e.g., reduce) either of the range measurements. Here, the Delta-RANGE value is instructive because it may indicate that both range measurements are from multipath signals. Since the longer range measurement is assumed to be associated with a multipath signal, the probability is reasonably high that the shorter range measurement is associated with a multipath signal since the two signals originate from approximately the same location.

It is noted that any of the above approaches may be combined with each other.

With reference to FIGS. 1 and 2A-B, attention is drawn to FIG. 3, which depicts a methodology 300 with steps for using timing data from co-located transmitters to compute a position estimate for a remote receiver.

At stage 310, for example, times of arrival corresponding to plurality of transmitters are measured. At stage 320, for example, times of arrival corresponding to pairs of co-located transmitters are identified. At stage 330, for example, time of arrival corresponding to only one transmitter of a pair of co-located transmitters may be identified and disregarded or a weight may apply to it to lower its effect during trilateration processing. Then, at stage 340, an estimate of position for a receiver using at least one time of arrival from each pair of transmitters may be determined.

The estimate from stage 340 may use the shorter of the two times of arrival for each pair of transmitters. Additionally or alternatively, the estimate from stage 340 may adjust (e.g., by weight or amount) the shorter time of arrival. Additionally or alternatively, the estimate from stage 340 may use the longer of the two times of arrival for each pair of transmitters, or an adjusted value of the longer time of arrival. Adjustments to and selection of times of arrival may be made based on a difference between the two times of arrival for each pair of transmitters.

Additional Aspects

One or more aspects may relate to systems and non-transitory computer usable media having a computer readable program code embodied therein that operate to implement any or all of the following method steps: measure data corresponding to times of arrival corresponding to signals received from a plurality of transmitters; identify, from the times of arrival, data corresponding to a first time of arrival corresponding to a first signal from a first transmitter of a first pair of co-located transmitters; identify, from the times of arrival, data corresponding to a second time of arrival corresponding to a second signal from a second transmitter of the first pair of co-located transmitters; and estimate the position of the receiver using first data, where the first data corresponds to at least one of the first time of arrival and the second time of arrival.

In accordance with some aspects, the first data corresponds to the shorter of the first time of arrival and the second time of arrival, but does not correspond to the longer of the first time of arrival and the second time of arrival. In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: adjust the first data based on an adjustment amount or an adjustment weight to generate first adjusted data, where the position of the receiver is estimated based on the first adjusted data; determine first difference data corresponding to a first difference between the first time of arrival and the second time of arrival; adjust the first data based on the first difference data to generate first adjusted data, where the position of the receiver is estimated based on the first adjusted data; determine first difference data corresponding to a first difference between the first time of arrival and the second time of arrival; generate an adjustment amount by applying a weight to the first difference data, where the absolute value of the weight is less than one; and adjust the first data by the adjustment amount to generate first adjusted data, where the position of the receiver is estimated based on the first adjusted data.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: adjust data corresponding to either or both of the first time of arrival and the second time of arrival before the position is estimated; and determine first difference data corresponding to a first difference between the first time of arrival and the second time of arrival; adjust data corresponding to either or both of the first time of arrival and the second time of arrival based on the first difference data; adjust data corresponding to either or both of the first time of arrival and the second time of arrival by at least one adjustment amount based on the first difference data; generate a weighted first difference data based on a weight and the first difference data; adjust data corresponding to either or both of the first time of arrival and the second time of arrival based on the weighted first difference data, where the absolute value of the weight is greater than zero and less than one; identify at least one adjustment from a database based on the first difference data; adjust data corresponding to either or both either or both of the first time of arrival and the second time of arrival based on the at least one adjustment amount; weight data corresponding to either or both either or both of the first time of arrival and the second time of arrival before the position is estimated; weight data corresponding to either or both either or both of the first time of arrival and the second time of arrival by at least one adjustment weight based on the first difference data; and identify the at least one weight from a database based on the first difference data, where the absolute value of the at least one weight is greater than zero and less than one, and the absolute value of the at least one weight is greater than one.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: determine a first estimated distance between the receiver and the first transmitter; determine a second estimated distance between the receiver and the second transmitter; determine a distance difference between the first estimated distance and the second estimated distance; determine a first difference data corresponding to a difference between the first time of arrival and the second time of arrival; adjust data corresponding to either or both of the first time of arrival and the second time of arrival based on a comparison of data associated with the distance difference to data associated with the first difference data; and adjust data corresponding to either or both of the first time of arrival and the second time of arrival by at least one adjustment amount or at least one adjustment weight when the comparison reveals the first difference data corresponds to a distance that exceeds the distance difference by a threshold amount, where the at least one adjustment amount or adjustment weight is based on the comparison.

In accordance with some aspects, where the first data corresponds to the shorter of the first time of arrival and the second time of arrival, where the position of the receiver is estimate using the first data corresponding to the shorter of the first time of arrival and the second time of-arrival. In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: adjust second data corresponding to the longer of the first time of arrival and the second time of arrival based on the first data; estimate the position of the receiver using the first data and the second data; estimating the position based on the first time of arrival and the second time of arrival; estimating the position based on an average of the first time of arrival and the second time of arrival.

In accordance with some aspects, where the plurality of transmitters further includes a third transmitter located at a third position that is substantially remote from a first position of the first transmitter and a second position of the second transmitter. In accordance with some aspects, where the plurality of transmitters includes a second pair of co-located transmitters having a fourth transmitter located at a fourth position and a fifth transmitter located at a fifth position, where the fourth and fifth positions are substantially remote from a first position of the first transmitter and a second position of the second transmitter.

In accordance with some aspects, where the plurality of transmitters further includes a third transmitter located at a third position that is substantially remote from a first position of the first transmitter and a second position of the second transmitter, and further includes a second pair of co-located transmitters having a fourth transmitter located at a fourth position and a fifth transmitter located at a fifth position, where the fourth and fifth positions are substantially remote from the first and second positions.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: determine that the first transmitter and the second transmitter are included in the first pair of co-located transmitters when a first position of the first transmitter and a second position of the second transmitter are within a threshold distance from each other; determine whether the first position and the second position are within the threshold distance from each other based information specifying a first latitude and a first longitude of the first transmitter, and a second latitude and second longitude of the second transmitter, where the threshold distance is five meters; and determine that the first transmitter and the second transmitter are included in the first pair of co-located transmitters based on a first identifier of the first transmitter and a second identifier of the second transmitter.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: estimate the position without using data corresponding to a third time of arrival from the third transmitter; identify, from the times of arrival, the third time of arrival; determine whether the times of arrival include another time of arrival from another transmitter that is co-located with the third transmitter; and upon determining that the times of arrival do not include the other time of arrival from the other transmitter that is co-located with the third transmitter, estimate the position without using data corresponding to the third time of arrival.

One or more aspects may relate to systems and computer program products comprising a non-transitory computer usable medium having a computer readable program code embodied therein that operate to implement any or all of the following method steps: receiving ranging signal information from a plurality of transmitters; identifying, from the ranging signal information, first ranging signal information from a first transmitter of a first pair of co-located transmitters, where the first transmitter is located at a first position; identifying, from the ranging signal information, second ranging signal information from a second transmitter of the first pair of co-located transmitters, where the second transmitter is located at a second position; and estimating the position of the receiver based one at least one of the first ranging signal information and the second ranging signal information.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: determining a first distance corresponding to the first ranging signal information; determining a second distance corresponding to the second ranging signal information; determining whether the first distance is less than the second distance, or whether the second distance is less than the first distance; upon determining that the first distance is less than the second distance, estimating the position of the receiver based on the first ranging signal information; upon determining that the second distance is less than the first distance, estimating the position of the receiver based on the second ranging signal information; upon determining that the first distance is less than the second distance, adjusting the first ranging signal information based on an adjustment amount or an adjustment weight to generate first adjusted ranging signal information, where the position of the receiver is estimated based on the first adjusted ranging signal information when the first distance is less than the second distance; upon determining that the second distance is less than the first distance, adjusting the second ranging signal information based on the adjustment amount or the adjustment weight to generate second adjusted ranging signal information, where the position of the receiver is estimated based on the second adjusted ranging signal information when the second distance is less than the first distance; computing a ranging difference between the first distance and the second distance; upon determining that the first distance is less than the second distance, adjusting the first ranging signal information based on the ranging difference to generate first adjusted ranging signal information, where the position of the receiver is estimated based on the first adjusted ranging signal information when the first distance is less than the second distance; upon determining that the second distance is less than the first distance, adjusting the second ranging signal information based on the ranging difference to generate second adjusted ranging signal information, where the position of the receiver is estimated based on the second adjusted ranging signal information when the second distance is less than the first distance; computing a ranging difference between the first distance and the second distance; generating an adjustment amount by applying a weight to the ranging difference, where the absolute value of the weight is less than one; upon determining that the first distance is less than the second distance, adjusting the first ranging signal information by the adjustment amount to generate first adjusted ranging signal information, where the position of the receiver is estimated based on the first adjusted ranging signal information when the first distance is less than the second distance; and upon determining that the second distance is less than the first distance, adjusting the second ranging signal information by the adjustment amount to generate second adjusted ranging signal information, where the position of the receiver is estimated based on the second adjusted ranging signal information when the second distance is less than the first distance.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: adjusting either or both of the first ranging signal information and the second ranging signal information before the position is estimated; computing a ranging difference between the first ranging signal information and the second ranging signal information; adjusting either or both of the first ranging signal information and the second ranging signal information based on the ranging difference; decreasing either or both of the first ranging signal information and the second ranging signal information by at least one adjustment amount based on the ranging difference; generating a weighted ranging difference based on a weight and the ranging difference; adjusting either or both of the first ranging signal information and the second ranging signal information based on the weighted ranging difference, where the absolute value of the weight is greater than zero and less than one; identifying at least one adjustment from a database based on the ranging difference; decreasing either or both of the first ranging signal information and the second ranging signal information based on the at least one adjustment amount; weighting either or both of the first ranging signal information and the second ranging signal information before the position is estimated; weighting either or both of the first ranging signal information and the second ranging signal information by at least one adjustment weight based on the ranging difference, where the absolute value of the at least one weight is greater than zero and less than one or where the absolute value of the at least one weight is greater than one; and identifying the at least one weight from a database based on the ranging difference.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: computing a first estimated distance between the receiver and the first transmitter; computing a second estimated distance between the receiver and the second transmitter; computing a distance difference between the first estimated distance and the second estimated distance; computing a ranging difference between the first ranging signal information and the second ranging signal information; comparing the distance difference to the ranging difference; adjusting either or both of the first ranging signal information and the second ranging signal information based on the comparing step; adjusting either or both of the first ranging signal information and the second ranging signal information by at least one adjustment amount when a comparison difference between the ranging difference and the distance difference exceeds a threshold amount, where the at least one adjustment amount is based on the comparison difference; and adjusting either or both of the first ranging signal information and the second ranging signal information by at least one adjustment weight when a comparison difference between the ranging difference and the distance difference exceeds a threshold amount, where the at least one adjustment weight is based on the comparison difference.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: determining whether a first distance corresponding to the first ranging signal information is less than a second distance corresponding to the second ranging signal information, or whether the second distance is less than the first distance; upon determining that the first distance is less than the second distance, estimating the position based on the first ranging signal information but not on the second ranging signal information, or upon determining that the second distance is less than the first distance, estimating the position based on the second ranging signal information but not on the first ranging signal information; determining whether a first distance corresponding to the first ranging signal information is less than a second distance corresponding to the second ranging signal information, or whether the second distance is less than the first distance; upon determining that the first distance is less than the second distance: adjusting the value of the second ranging signal information to the value of value of the first ranging signal information, and estimating the position based on the first ranging signal information and the adjusted value of the second ranging signal information, or upon determining that the second distance is less than the first distance: adjusting the value of the first ranging signal information to the value of value of the second ranging signal information, and estimating the position based on the second ranging signal information and the adjusted value of the first ranging signal information; estimating the position based on the first ranging signal information and the second ranging signal information; and estimating the position based on an average of the first ranging signal information and the second ranging signal information.

In accordance with some aspects, where the plurality of transmitters further includes a third transmitter located at a third position that is substantially remote from the first and second positions. In accordance with some aspects, where the plurality of transmitters includes a second pair of co-located transmitters having a fourth transmitter located at a fourth position and a fifth transmitter located at a fifth position, where the fourth and fifth positions are substantially remote from the first and second positions. In accordance with some aspects, where the plurality of transmitters further includes a third transmitter located at a third position that is substantially remote from the first and second positions, and further includes a second pair of co-located transmitters having a fourth transmitter located at a fourth position and a fifth transmitter located at a fifth position, where the fourth and fifth positions are substantially remote from the first and second positions.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: determining that the first transmitter and the second transmitter are included in the first pair of co-located transmitters when the first position and the second position are within a threshold distance from each other; determining whether the first position and the second position are within the threshold distance from each other based information specifying a first latitude and a first longitude of the first transmitter, and a second latitude and second longitude of the second transmitter, where the threshold distance is five meters; determining that the first transmitter and the second transmitter are included in the first pair of co-located transmitters based on first identifying information of the first transmitter and second identifying information of the second transmitter.

In accordance with some aspects, the methods, systems and computer usable media may operate to implement any or all of the following method steps: performing the steps of estimating without using third ranging signal information from the third transmitter; identifying, from the ranging signal information, the third ranging signal information from the third transmitter; determining whether the ranging signal information includes other ranging signal information from another transmitter that is co-located with the third transmitter; upon determining that the ranging signal information does not include the other ranging signal information from the other transmitter that is co-located with the third transmitter, performing the estimating step without using the third ranging signal information.

Supporting Aspects

Various aspects relate to disclosures of other patent applications, patent publications, or issued patents. For example, each of the following applications, publications, and patents are incorporated by reference in their entirety for any and all purposes: United States Utility patent application Ser. No. 13/412,487, entitled WIDE AREA POSITIONING SYSTEMS, filed on Mar. 5, 2012; U.S. Utility patent Ser. No. 12/557,479 (now U.S. Pat. No. 8,130,141), entitled WIDE AREA POSITIONING SYSTEM, filed Sep. 10, 2009; United States Utility patent application Ser. No. 13/412,508, entitled WIDE AREA POSITIONING SYSTEM, filed Mar. 5, 2012; United States Utility patent application Ser. No. 13/296,067, entitled WIDE AREA POSITIONING SYSTEMS, filed Nov. 14, 2011; Application Serial No. PCT/US12/44452, entitled WIDE AREA POSITIONING SYSTEMS (WAPS), filed Jun. 28, 2011); U.S. patent application Ser. No. 13/535,626, entitled CODING IN WIDE AREA POSITIONING SYSTEMS (WAPS), filed Jun. 28, 2012; U.S. patent application Ser. No. 13/565,732, entitled CELL ORGANIZATION AND TRANSMISSION SCHEMES IN A WIDE AREA POSITIONING SYSTEM (WAPS), filed Aug. 2, 2012; U.S. patent application Ser. No. 13/565,723, entitled CELL ORGANIZATION AND TRANSMISSION SCHEMES IN A WIDE AREA POSITIONING SYSTEM (WAPS), filed Aug. 2, 2012; U.S. patent application Ser. No. 13/831,740, entitled SYSTEMS AND METHODS CONFIGURED TO ESTIMATE RECEIVER POSITION USING TIMING DATA ASSOCIATED WITH REFERENCE LOCATIONS IN THREE-DIMENSIONAL SPACE, filed Mar. 14, 2013. The above applications, publications and patents may be individually or collectively referred to herein as “incorporated reference(s)”, “incorporated application(s)”, “incorporated publication(s)”, “incorporated patent(s)” or otherwise designated. The various aspect, details, devices, systems, and methods disclosed herein may be combined with disclosures in any of the incorporated references in accordance with various embodiments.

This disclosure relates generally to positioning systems and methods for providing signaling for position determination and determining high accuracy position/location information using a wide area transmitter array of transmitters in communication with receivers such as in cellular phones or other portable devices with processing components, transceiving capabilities, storage, input/output capabilities, and other features.

Positioning signaling services associated with certain aspects may utilize broadcast-only transmitters that may be configured to transmit encrypted positioning signals. The transmitters (which may also be denoted herein as “towers” or “beacons”) may be configured to operate in an exclusively licensed or shared licensed/unlicensed radio spectrum; however, some embodiments may be implemented to provide signaling in unlicensed shared spectrum. The transmitters may transmit signaling in these various radio bands using novel signaling as is described herein or in the incorporated references. This signaling may be in the form of a proprietary signal configured to provide specific data in a defined format advantageous for location and navigation purposes. For example, the signaling may be structured to be particularly advantageous for operation in obstructed environments, such as where traditional satellite position signaling is attenuated and/or impacted by reflections, multipath, and the like. In addition, the signaling may be configured to provide fast acquisition and position determination times to allow for quick location determination upon device power-on or location activation, reduced power consumption, and/or to provide other advantages.

The receivers may be in the form of one or more user devices, which may be any of a variety of electronic communication devices configured to receive signaling from the transmitters, as well as optionally be configured to receive GPS or other satellite system signaling, cellular signaling, Wi-Fi signaling, Wi-Max signaling, Bluetooth, Ethernet, and/or other data or information signaling as is known or developed in the art. The receivers may be in the form of a cellular or smart phone, a tablet device, a PDA, a notebook or other computer system, and/or similar or equivalent devices. In some embodiments, the receivers may be a standalone location/positioning device configured solely or primarily to receive signals from the transmitters and determine location/position based at least in part on the received signals. As described herein, receivers may also be denoted herein as “User Equipment” (UE), handsets, smart phones, tablets, and/or simply as a “receiver.”

The transmitters may be configured to send transmitter output signals to multiple receiver units (e.g., a single receiver unit is shown in certain figures for simplicity; however, a typical system will be configured to support many receiver units within a defined coverage area) via communication links). The transmitters may also be connected to a server system via communication links, and/or may have other communication connections to network infrastructure, such as via wired connections, cellular data connections, Wi-Fi, Wi-Max, or other wireless connections, and the like.

Various embodiments of a wide area positioning system (WAPS), described herein or in the incorporated references, may be combined with other positioning systems to provide enhanced location and position determination. Alternately, or in addition, a WAPS system may be used to aid other positioning systems. In addition, information determined by receivers of WAPS systems may be provided via other communication network links, such as cellular, Wi-Fi, pager, and the like, to report position and location information to a server system or systems, as well as to other networked systems existing on or coupled to network infrastructure.

For example, in a cellular network, a cellular backhaul link may be used to provide information from receivers to associated cellular carriers and/or others via network infrastructure. This may be used to quickly and accurately locate the position of receiver during an emergency, or may be used to provide location-based services or other functions from cellular carriers or other network users or systems.

It is noted that, in the context of this disclosure, a positioning system is one that localizes one or more of latitude, longitude, and altitude coordinates, which may also be described or illustrated in terms of one, two, or three dimensional coordinate systems (e.g., x, y, z coordinates, angular coordinates, vectors, and other notations). In addition, it is noted that whenever the term ‘GPS’ is referred to, it is done so in the broader sense of Global Navigation Satellite Systems (GNSS) which may include other satellite positioning systems such as GLONASS, Galileo and Compass/Beidou. In addition, as noted previously, in some embodiments other positioning systems, such as terrestrially based systems, may be used in addition to or in place of satellite-based positioning systems.

Embodiments of WAPS include multiple transmitters configured to broadcast WAPS data positioning information, and/or other data or information, in transmitter output signals to the receivers. The positioning signals may be coordinated so as to be synchronized across all transmitters of a particular system or regional coverage area, and may use a disciplined GPS clock source for timing synchronization. WAPS data positioning transmissions may include dedicated communication channel resources (e.g., time, code and/or frequency) to facilitate transmission of data required for trilateration, notification to subscriber/group of subscribers, broadcast of messages, and/or general operation of the WAPS system. Additional disclosure regarding WAPS data positioning transmissions may be found in the incorporated references.

In a positioning system that uses time difference of arrival or trilateration, the positioning information typically transmitted includes one or more of precision timing sequences and positioning signal data, where the positioning signal data includes the location of transmitters and various timing corrections and other related data or information. In one WAPS embodiment, the data may include additional messages or information such as notification/access control messages for a group of subscribers, general broadcast messages, and/or other data or information related to system operation, users, interfaces with other networks, and other system functions. The positioning signal data may be provided in a number of ways. For example, the positioning signal data may be modulated onto a coded timing sequence, added or overlaid over the timing sequence, and/or concatenated with the timing sequence.

Data transmission methods and apparatus described herein may be used to provide improved location information throughput for the WAPS. In particular, higher order modulation data may be transmitted as a separate portion of information from pseudo-noise (PN) ranging data. This may be used to allow improved acquisition speed in systems employing CDMA multiplexing, TDMA multiplexing, or a combination of CDMA/TDMA multiplexing. The disclosure herein is illustrated in terms of WAPS in which multiple towers broadcast synchronized positioning signals to UEs and, more particularly, using towers that are terrestrial. However, the embodiments are not so limited, and other systems within the spirit and scope of the disclosure may also be implemented.

In an exemplary embodiment, a WAPS system uses coded modulation sent from a tower or transmitter, such as transmitter, called spread spectrum modulation or pseudo-noise (PN) modulation, to achieve wide bandwidth. The corresponding receiver unit, such as receiver, includes one or more modules to process such signals using a despreading circuit, such as a matched filter or a series of correlators. Such a receiver produces a waveform which, ideally, has a strong peak surrounded by lower level energy. The time of arrival of the peak represents the time of arrival of the transmitted signal at the receiver. Performing this operation on a multiplicity of signals from a multiplicity of towers, whose locations are accurately known, allows determination of the receivers location via trilateration. Various additional details related to WAPS signal generation in a transmitter, along with received signal processing in a receiver are described herein or in the incorporated references.

Transmitters may include various blocks for performing associated signal reception and/or processing. For example, a transmitter may include one or more GPS modules for receiving GPS signals and providing location information and/or other data, such as timing data, dilution of precision (DOP) data, or other data or information as may be provided from a GPS or other positioning system, to a processing module. Other modules for receiving satellite or terrestrial signals and providing similar or equivalent output signals, data, or other information may alternately be used in various embodiments. GPS or other timing signals may be used for precision timing operations within transmitters and/or for timing correction across the WAPS system.

Transmitters may also include one or more transmitter modules (e.g., RF transmission blocks) for generating and sending transmitter output signals as described subsequently herein. A transmitter module may also include various elements as are known or developed in the art for providing output signals to a transmit antenna, such as analog or digital logic and power circuitry, signal processing circuitry, tuning circuitry, buffer and power amplifiers, and the like. Signal processing for generating the output signals may be done in the a processing module which, in some embodiments, may be integrated with another module or, in other embodiments, may be a standalone processing module for performing multiple signal processing and/or other operational functions.

One or more memories may be coupled with a processing module to provide storage and retrieval of data and/or to provide storage and retrieval of instructions for execution in the processing module. For example, the instructions may be instructions for performing the various processing methods and functions described subsequently herein, such as for determining location information or other information associated with the transmitter, such as local environmental conditions, as well as to generate transmitter output signals to be sent to the user devices.

Transmitters may further include one or more environmental sensing modules for sensing or determining conditions associated with the transmitter, such as, for example, local pressure, temperature, or other conditions. In an exemplary embodiment, pressure information may be generated in the environmental sensing module and provided to a processing module for integration with other data in transmitter output signals as described subsequently herein. One or more server interface modules may also be included in a transmitter to provide an interface between the transmitter and server systems, and/or to a network infrastructure.

Receivers may include one or more GPS modules for receiving GPS signals and providing location information and/or other data, such as timing data, dilution of precision (DOP) data, or other data or information as may be provided from a GPS or other positioning system, to a processing module (not shown). Of course, other Global Navigation Satellite Systems (GNSS) are contemplated, and it is to be understood that disclosure relating to GPS may apply to these other systems. Of course, any location processor may be adapted to receive and process position information described herein or in the incorporated references.

Receivers may also include one or more cellular modules for sending and receiving data or information via a cellular or other data communications system. Alternately, or in addition, receivers may include communications modules for sending and/or receiving data via other wired or wireless communications networks, such as Wi-Fi, Wi-Max, Bluetooth, USB, or other networks.

Receivers may include one or more position/location modules for receiving signals from terrestrial transmitters, and processing the signals to determine position/location information as described subsequently herein. A position module may be integrated with and/or may share resources such as antennas, RF circuitry, and the like with other modules. For example, a position module and a GPS module may share some or all radio front end (RFE) components and/or processing elements. A processing module may be integrated with and/or share resources with the position module and/or GPS module to determine position/location information and/or perform other processing functions as described herein. Similarly, a cellular module may share RF and/or processing functionality with an RF module and/or processing module. A local area network (LAN) module may also be included.

One or more memories may be coupled with processing module and other modules to provide storage and retrieval of data and/or to provide storage and retrieval of instructions for execution in the processing module. For example, the instructions may perform the various processing methods and functions described herein or in the incorporated references.

Receivers may further include one or more environmental sensing modules (e.g., inertial, atmospheric and other sensors) for sensing or determining conditions associated with the receiver, such as, for example, local pressure, temperature, movement, or other conditions, that may be used to determine the location of the receiver. In an exemplary embodiment, pressure information may be generated in such an environmental sensing module for use in determining location/position information in conjunction with received transmitter, GPS, cellular, or other signals.

Receivers may further include various additional user interface modules, such as a user input module which may be in the form of a keypad, touchscreen display, mouse, or other user interface element. Audio and/or video data or information may be provided on an output module (not shown), such as in the form or one or more speakers or other audio transducers, one or more visual displays, such as touchscreens, and/or other user I/O elements as are known or developed in the art. In an exemplary embodiment, such an output module may be used to visually display determined location/position information based on received transmitter signals, and the determined location/position information may also be sent to a cellular module to an associated carrier or other entity.

The receiver may include a signal processing block that comprises a digital processing block configured to demodulate the received RF signal from the RF module, and also to estimate time of arrival (TOA) for later use in determining location. The signal processing block may further include a pseudorange generation block and a data processing block. The pseudorange generation block may be configured to generate “raw’ positioning pseudorange data from the estimated TOA, refine the pseudorange data, and to provide that pseudorange data to the position engine, which uses the pseudorange data to determine the location of the receiver. The data processing block may be configured to decode the position information, extract packet data from the position information and perform error correction (e.g., CRC) on the data. A position engine of a receiver may be configured to process the position information (and, in some cases, GPS data, cell data, and/or LAN data) in order to determine the location of the receiver within certain bounds (e.g., accuracy levels, etc.). Once determined, location information may be provided to applications. One of skill in the art will appreciate that the position engine may signify any processor capable of determining location information, including a GPS position engine or other position engine.

Variations of Implementation

The various components, modules, and functions described herein can be located together or in separate locations. Communication paths couple the components and include any medium for communicating or transferring files among the components. The communication paths include wireless connections, wired connections, and hybrid wireless/wired connections. The communication paths also include couplings or connections to networks including local area networks (LANs), metropolitan area networks (MANs), wide area networks (WANs), proprietary networks, interoffice or backend networks, and the Internet. Furthermore, the communication paths include removable fixed mediums like floppy disks, hard disk drives, and CD-ROM disks, as well as flash RAM, Universal Serial Bus (USB) connections, RS-232 connections, telephone lines, buses, and electronic mail messages.

Aspects of the systems and methods described herein may be implemented as functionality programmed into any of a variety of circuitry, including programmable logic devices (PLDs), such as field programmable gate arrays (FPGAs), programmable array logic (PAL) devices, electrically programmable logic and memory devices and standard cell-based devices, as well as application specific integrated circuits (ASICs). Some other possibilities for implementing aspects of the systems and methods include: microcontrollers with memory (such as electronically erasable programmable read only memory (EEPROM)), embedded microprocessors, firmware, software, etc. Furthermore, aspects of the systems and methods may be embodied in microprocessors having software-based circuit emulation, discrete logic (sequential and combinatorial), custom devices, fuzzy (neural) logic, quantum devices, and hybrids of any of the above device types. The underlying device technologies may be provided in a variety of component types, e.g., metal-oxide semiconductor field-effect transistor (MOSFET) technologies like complementary metal-oxide semiconductor (CMOS), bipolar technologies like emitter-coupled logic (ECL), polymer technologies (e.g., silicon-conjugated polymer and metal-conjugated polymer-metal structures), mixed analog and digital, etc.

It should be noted that any system, method, and/or other components disclosed herein may be described using computer aided design tools and expressed (or represented), as data and/or instructions embodied in various computer-readable media, in terms of their behavioral, register transfer, logic component, transistor, layout geometries, and/or other characteristics. Computer-readable media in which such formatted data and/or instructions may be embodied include, but are not limited to, non-volatile storage media in various forms (e.g., optical, magnetic or semiconductor storage media) and carrier waves that may be used to transfer such formatted data and/or instructions through wireless, optical, or wired signaling media or any combination thereof. Examples of transfers of such formatted data and/or instructions by carrier waves include, but are not limited to, transfers (uploads, downloads, e-mail, etc.) over the Internet and/or other computer networks via one or more data transfer protocols (e.g., HTTP, HTTPs, FTP, SMTP, WAP, etc.). When received within a computer system via one or more computer-readable media, such data and/or instruction-based expressions of the above described components may be processed by a processing entity (e.g., one or more processors) within the computer system in conjunction with execution of one or more other computer programs.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in a sense of “including, but not limited to.” Words using the singular or plural number also include the plural or singular number respectively. Additionally, the words “herein,” “hereunder,” “above,” “below,” and words of similar import, when used in this application, refer to this application as a whole and not to any particular portions of this application. When the word “or” is used in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list and any combination of the items in the list.

The above description of embodiments of the systems and methods is not intended to be exhaustive or to limit the systems and methods to the precise forms disclosed. While specific embodiments of, and examples for, the systems and methods are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the systems and methods, as those skilled in the relevant art will recognize. The teachings of the systems and methods provided herein can be applied to other systems and methods, not only for the systems and methods described above. The elements and acts of the various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the systems and methods in light of the above detailed description.

One of skill in the art will appreciate that the processes shown in the Drawings and described herein are illustrative, and that there is no intention to limit this disclosure to the order of stages shown. Accordingly, stages may be removed and rearranged, and additional stages that are not illustrated may be carried out within the scope and spirit of the invention.

In one or more exemplary embodiments, the functions, methods and processes described may be implemented in whole or in part in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer.

By way of example, and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill in the art would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the disclosure.

The various illustrative logical blocks, modules, processes, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps or stages of a method, process or algorithm in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language of the claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. A phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a; b; c; a and b; a and c; b and c; and a, b and c.

The previous description of the disclosed aspects is provided to enable any person skilled in the art to make or use the present disclosure. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the aspects shown herein but is to be accorded the widest scope consistent with the appended claims and their equivalents.

As used herein, computer program products comprising computer-readable media including all forms of computer-readable medium except, to the extent that such media is deemed to be non-statutory, transitory propagating signals.

While various embodiments of the present invention have been described in detail, it may be apparent to those skilled in the art that the present invention can be embodied in various other forms not specifically described herein. Therefore, the protection afforded the present invention should only be limited in accordance with the following claims. 

1. A method for estimating a position of receiver, the method comprising: extracting information from a first ranging signal received from a first transmitter; extracting information from a second ranging signal received from a second transmitter; determining a first location of the first transmitter; determining a second location of the second transmitter, wherein the first location and the second location are separated by no more than 100 meters; and determining an estimated position of the receiver based on one or more relationships between the information extracted from the first and second ranging signals and information corresponding to the first and second locations.
 2. The method of claim 1, wherein the method comprises: determining a weight based on the one or more relationships; and using the weight to determine the estimated position.
 3. The method of claim 1, wherein the method comprises: determining a time bias based on the one or more relationships; and using the time bias to determine the estimated position.
 4. The method of claim 1, wherein the method comprises: determining a first line-of-sight distance between an initial estimate of the receiver's position and the first location of the first transmitter; determining a second line-of-sight distance between the initial estimate of the receiver's position and the second location of the second transmitter; determining a first path distance between the receiver and the first location of the first transmitter, wherein the first path distance corresponds to a first distance travel by the first ranging signal; determining a second path distance between the receiver and the second location of the second transmitter, wherein the second path distance corresponds to a second distance travel by the second ranging signal; and determining said estimated position of the receiver using the first line-of-sight distance, the second line-of-sight distance, the first path distance, and the second path distance.
 5. The method of claim 4, wherein the method comprises: determining a first measure of difference between the first and second path distances; determining a second measure of difference between the first and second line-of-sight distances; and determining if the first measure exceeds the second measure by a first amount.
 6. The method of claim 5, wherein if the first measure exceeds the second measure by a first amount, the method further comprises: based on determining that the first path distance is less than the second path distance: determining the estimated position using the information extracted from the first ranging signal and without using the information extracted from the second ranging signal; or adjusting the information extracted from the second ranging signal, wherein the estimated position is determined using the adjusted information extracted from the second ranging signal; and based on determining that the second path distance is less than the first path distance: determining the estimated position using the information extracted from the second ranging signal and without using the information extracted from the first ranging signal; or adjusting the information extracted from the first ranging signal, wherein the estimated position is determined using the adjusted information extracted from the first ranging signal.
 7. The method of claim 5, wherein the first ranging signal and the second ranging signal are concurrently transmitted, and wherein if the first measure exceeds the second measure by the first amount, the method further comprises: based on determining that the first ranging signal arrived at the receiver before the second ranging signal arrived at the receiver: determining the estimated position using the information extracted from the first ranging signal and without using the information extracted from the second ranging signal; or adjusting the information extracted from the second ranging signal, wherein the estimated position is determined using the adjusted information extracted from the second ranging signal; and based on determining that the second ranging signal arrived at the receiver before the first ranging signal arrived at the receiver: determining the estimated position using the information extracted from the second ranging signal and without using the information extracted from the first ranging signal; or adjusting the information extracted from the first ranging signal, wherein the estimated position is determined using the adjusted information extracted from the first ranging signal.
 8. The method of claim 1, wherein the first ranging signal and the second ranging signal are concurrently transmitted, and wherein the method comprises: based on determining that the first ranging signal arrived at the receiver before the second ranging signal arrived at the receiver: determining the estimated position using the information extracted from the first ranging signal and without using the information extracted from the second ranging signal, or adjusting the information extracted from the second ranging signal, wherein the estimated position is determined using the adjusted information extracted from the second ranging signal; and based on determining that the second ranging signal arrived at the receiver before the first ranging signal arrived at the receiver: determining the estimated position using the information extracted from the second ranging signal and without using the information extracted from the first ranging signal, or adjusting the information extracted from the first ranging signal, wherein the estimated position is determined using the adjusted information extracted from the first ranging signal.
 9. A system comprising one or more processors that perform the method of claim
 1. 10. A non-transitory machine-readable medium embodying program instructions adapted to be executed to implement the method of claim
 1. 